Photothermal heterodyne imaging and absorption spectroscopy of individual nonfluorescent nano-objects

An all-optical method called photothermal heterodyne imaging (PHI) is developed that allows for the detection of individual nano-objects such as gold nanoparticles with diameter down to 1.4 /spl mu/m (67 atoms) as well as nonluminescent semiconductor nanocrystals. This observation of intrinsic size effects in the optical response of gold nanoparticles is analysed within the frame of Mie theory using a size-dependent surface damping term in the dielectric constant.